# Do physicist's consider themselve's one of instruments in an experiment?

1. Jan 14, 2006

### quantumcarl

Do Physicist's consider themselve's as being one of the instruments in an experiment? Or, as, at least as one of the conditions effecting the outcome? Are these conditions included in the final report?

I notice in some of the quantum physics experiments I've read there is a lot of care taken to be sure that those performing the experiment are unaware of certain effects or information they are going to be observing until it is right in their lap, so to speak. This was a quantum teleportation experiement or something. This seems to be treating the observer/scientist as one of the conditions and, perhaps, even an instrument to the whole process. I am close here?

2. Jan 15, 2006

### Ivan Seeking

Staff Emeritus
An observation constitutes a measurement on the system. According to not only Heisenberg's principle - knowledge of one parameter limits knowledge of another - but also the deeper stuff from QM

The Measurment Problem
http://plato.stanford.edu/entries/qt-measurement/
and
Entaglement
http://plato.stanford.edu/entries/qt-epr/
http://plato.stanford.edu/entries/qt-entangle/,

the observer affects the results, so it could have been that this was the issue. Generally speaking, the idea is that once you observe [measure] something, you collapse the system - the wave function - into a unique state, or "Eigenstate".

Last edited: Jan 15, 2006
3. Jan 15, 2006

### quantumcarl

Ah, so that's what all the entanglement is about.

The other thrust to do with this thread is how can we assess our physicist's or other scientist's ability to observe? Are there eye exams? Are there blood tests and other examinations that certify the ability of a physicist to observe and observe accurately? Is there manditory training in the methods of using the physicist's body as an efficient instrument of observation?

I earlier compared high-end physicists to hockey players like Gretsky or Messier. Both disciplines have goals in mind. Both concentrate with great focus on the methods and practices that go toward acheiving their goals. Neither disciplines need dally in philosophy except with respect to ethics and that can be left up to their lawers!

However, as far as I know, physicists are not required to submit to a complete physical before they begin their observations and a carreer in physics.

This may sound trivial but, I would think that the better physical shape a physicist is in... the more accurate the results of their experiments and of their observations of those experiments.

With regard to this thread being moved, this is a full discloser of how it was handled via PFmessaging:

4. Jan 16, 2006

### vanesch

Staff Emeritus
I think there's some confusion here. The day that a physicist has to report his mental state (health?) into his publications, I think physics went down the drain !
There are several possible connections to what you write.

The first one is probably the Many Worlds Interpretation of QM (of which I'm a proponent, in the sense that I think that it is the only view which is entirely consistent with the *current* formalism of quantum theory).
It states in fact that one should discriminate between the *body* of an observer and the observer itself (its mental state). The body of the observer, as a physical structure, entangles with the quantum system through the unitarily described physical interactions imposed by the entire measurement chain. As such, the body "sees" all possible outcomes. It sees as well the result "5" as the result "2", the "click" and the absense of a click.
However, the observer himself is only aware of ONE of these bodystates - this is what introduces, for the observer, the APPARENT collapse of the state into one of the eigenstates, and the probabilistic aspect of his observations.
Clearly, as such, the observer's body is part of the system under study.

Another aspect is maybe simply the "double blind" test as used in medicine. In order to avoid observers from consciously or unconsciously to prefer certain outcomes and to bias the measurement results, it is best that, during the data taking, they are not aware of the result they are supposed to obtain in order to comfort their personal preferences. But although this may play a role in medicine (where there are things such as the placebo effect, even induced by the doctor), in a well-designed data acquisition system that shouldn't play a role in a physics experiment!

5. Jan 16, 2006

### quantumcarl

This is great. When you say the observer or
doesn't this mean the body of the observer should be subject to measurements and the measurements recorded as well? I mean... in your own words...

so then, perhaps it needs to be studied in terms as an integral part of the system.

I don't mean this to question results so much as I am advocating "finely tuned" instruments be associated with the pursuit of knowledge. I mean the physicist wouldn't get very good results if the linear accelerator was curved... or the cyclotron (sp) was out of whack.

I don't know if this quote relates what I'm saying here, and its from kind of dippy science website but... here it is:

(from:http://www.geocities.com/roquanta/)

6. Jan 16, 2006

### vanesch

Staff Emeritus
Well, the "observer" is the one who observes the result ; or the one who observes the observer of the results, or... in other words, YOU.

But really, in practice, (even in an MWI view), you do not need to bother about this, and you do not need to consider the mental state of the experimenter. Note that I make a distinction between the "experimenter" which is the guy/girl who made the apparatus work, and who wrote down the paper ; and the observer, who is the *ultimate* consumer of the information, who is nothing else but YOU ; after all, in MWI, even the written paper is in a state of superposition. It is only when YOU read the paper, and mentally are aware of its content, that it takes on a definite form wrt to YOU. (and not even wrt to your body, which will have read ALL variants of the paper!) As such, nowhere in the chain, the *mental* state of the experimenter came into discussion (unless it was a mentally disordered one, or an incompetent one, and did a bad experiment, or wrote down nonsense). So the only mental state that needs eventually to come into the picture, is your own :-)

And really, really, we take it that from the moment that things get macroscopic, you can trace down the entire chain (from your mental awareness of one of your bodystates, to the state of the paper, to the state of the experimenter writing the paper, to the state of the measurement apparatus), and simply consider that classical rules apply from the moment that irreversible entanglement with the environment took place. From that moment on, even YOUR mental state cannot influence the outcome of the experiment, nor can the experimenter's mental state do so. And things get sane again

7. Jan 16, 2006

### quantumcarl

Everything you've written in your post is all holding together nicely with the exception of one thing I found in the quote provided.

My mental state may or may not influence the outcome of an experiment but an experiment itself is performed for the sole purpose of observation and... observation requires the fundamental mental state of awareness.

Awareness is a mental state that can be greatly enhanced or can be functioning poorly, depending upon the condtion(s) of individual generating the awareness.

I mean, can you see Dr. Bohr going through some kind of hearing like they do in congress only in this one there is a barrage of psych exams and physicals!?!?!?:rofl:

I'm almost seeing a space camp for physicists, sort of. Look at what astronaughts have to go through. You guys are pushing similar boundaries.

8. Jan 17, 2006

### Ivan Seeking

Staff Emeritus
This is a new twist on things for me. What forces you and I to agree on the eigenstate of the system? You seem to be saying that the "apparent" collapse of the wave function is unique to each observer.

9. Jan 17, 2006

### vanesch

Staff Emeritus
Indeed. Suppose you and I are going to watch a quantum experiment: we are going to look at the meter that will measure the state u|a> + v|b> of some system. Before all this interacts, we have:

|bodyivan0>|bodyvanesch0>|meter0>(u|a> + v|b> )

Now, the meter interacts (but we don't look yet) through its unitary interaction with the system:

|bodyivan0>|bodyvanesch0>(u|metera>|a> + v|meterb>|b> )

So the state of the meter got entangled with the system. In state |metera> the meter says on its display that the state was a, and in |meterb> the meter says on its display that the state was b.

Now you and I look (we can do this in two steps, or all together). We have (also unitary, the process of looking):

u |bodyivanA>|bodyvaneschA> |metera> |a> + v |bodyivanB>|bodyvaneschB> |meterb> |b>

But I am supposed to be only aware of one bodystate (say, A). You are supposed to be only aware of one bodystate (say, B, to make it spicy). I'll indicate with an asterix the state I'm aware off (and with a $sign, the state you are aware off): u |bodyivanA>|bodyvaneschA*> |metera> |a> + v |bodyivanB$>|bodyvaneschB> |meterb> |b>

I'm aware of a bodystate in which I'm in contact with a bodystate of Ivan which saw A, I am in contact with a meter who says "a" and the state of the system seems to be |a>. It looks as if the state collapsed into the "a" outcome for me. So if I ask the Ivan I'm in contact with, what he saw, he will say A, and will have all the memories of Ivan before the experiment.

You are aware of a bodystate in which you saw B, you are in contact with a bodystate of mine which saw B, the meter saw b, and the state seems to be |b>. It seems that the state collapsed into "b" for you.

There's no way for me (by any observable phenomenon) that your bodystate A is not the one you are aware off, and the same for you about my bodystate B.

The only thing one needs to complete the story is to say that the Born rule dictates the probability of choosing a body state or another to be aware off.

You can now discuss until midnight whether or not this other bodystate is a new consciousness or not. The only point is that this POV "you are aware of one of your bodystates" explains the apparent collapse, and (I did this a few times here) can also explain without FTL paradoxes, the Bell type experiments, and quantum eraser experiments.

10. Jan 17, 2006

### quantumcarl

And my question with regard to the thread would be

'did the differing mental states of awareness in the body states of * and \$ contribute to the differences of observation or was there a meter mal-function or did the (quantum) state of the system observed act in a natural manner' and give the separate results?

11. Jan 17, 2006

### Ivan Seeking

Staff Emeritus
Aha!!! I thought that you were going to avoid this problem.

12. Jan 18, 2006

### vanesch

Staff Emeritus
It is not a problem. You can never find out if the bodystate of another one is "inhabited by the original consciousness or not". You can only interact through physical interactions with that bodystate, and that will react the same whether or not it is the source of subjective experience for the original being or not. It is just not "the person you knew 5 minutes ago", but it is a perfect copy of it (with or without its own subjective experience, take your pick), up to the difference in memory state of the outcome of the experience.

As a classical counterpart, consider that I'm Speedy Gonzales, and in a fraction of a second (you don't notice it), I take away a friend of yours, copy his body exactly, and put that copy or the original at the place where I took the original. No way for you to find out which one it is. The copy will act exactly as you would expect the original to act. The copy will not know it is a copy.

13. Jan 19, 2006

### quantumcarl

You've raised a point here that is so integral to the thread.

With an instrument, the only changes that will occur in it are mechanical, physical little bothers like the glass breaking on the VU meter or a wire shorting out or like the focus on a microscope... etc... these are the changes that can occur with an instrument.

With the experimenter the changes are on-going. The experimenter's awareness is fluxuating... the things they are aware of is changing with time and the amount of knowledge the gather about their environment is growing at an alarming rate even if they are not aware of it.

Can this changing "consciousness" as it is often called be figured (with the precision of instrument measurments) into the idea of the experimenter being an instrument?

This all reminds me of when a linear accelerator was out of commission. The techs were sure they'd killed a patient with radiation. The hunt was on for the flaw in the accelerator... or the lazer guidance system or whatever........ in the end it turned out to be the gantry that holds the patient in place for treatment.

The gantry had cracked under the constant strain of so many patient's weights. It took an electrical engineer to even think of looking at the alignment of the gantry... the physicists were too hung up with the whole instrumentation and voodoo radiation to look for the cause in some obvious spots.

14. Jan 19, 2006

### Ivan Seeking

Staff Emeritus
What kind of following does MWT have these days? Really, I have had a hard time getting anyone to talk about it.

Is this the only interpretation, or are there various approaches with signficant differences between them.

How do we handle conservation of energy with all of these universes popping up? Where does the energy for the copies come from?

Last edited: Jan 20, 2006
15. Jan 20, 2006

### Ivan Seeking

Staff Emeritus
I read Other Worlds, by Davies, just before staring my upper division Quantum series. I thought this guy had to be absolutely nuts so I asked about it the first day of class; fully expecting the Prof to laugh, or something similar. Instead he said appox: "Anything that Davies says is gold". I about fell out of my chair!!!

Last edited: Jan 20, 2006
16. Jan 20, 2006

### vanesch

Staff Emeritus
As far as I know, many leading physicists in the fundamental domains in one way or another adhere to it, even if only implicitly. The reason for that is that they seem to adhere to unitarity as a fundamental axiom. As I pointed out a few times, if you can consider things like Hawking does, taking superpositions of spacetimes with a black hole forming and evaporating, and the spacetime where the black hole didn't form, and calculate path integrals (make the terms interfere) over the different possibilities, it seems to me that you take MWI seriously.
All quantum cosmologists seem to take this viewpoint too (the concept of quantum state of the universe has only a meaning in an MWI setting).
Even Penrose says that he thinks that MWI is the only view compatible with unitary quantum theory ; but he thinks that unitary quantum theory will turn out not to be correct, but only a linearized approximation to a theory where gravity will play the role of the non-linear agent that will introduce a genuine objective collapse. Personally, I take that suggestion seriously. I'm indeed not claiming that MWI is ultimately true ! I'm claiming that it is the most natural interpretation of unitary quantum theory.

All the work on decoherence theory (Zeh, Zurek, Joos,...) has only a meaning in the framework of MWI. Indeed, how could you consider the quantum state of the environment and the measurement apparatus otherwise ?

That said, there are of course still many people taking the collapse view seriously. I think that's because they didn't give it enough thought . Indeed, I know quite some particle physicists who claim that: 1) the quantum state is the physical state ; 2) collapse is something that happens to the quantum state in the measurement apparatus ; 3) locality holds, and ALL laws of physics are to be formulated in a Lorentz-invariant way. This is funny of course, because you cannot formulate collapse in a Lorentz-invariant way! On the other hand, you CAN formulate unitary physics in a Lorentz-invariant way, and that's what they do all the time.

Another viewpoint is that QM is just a mathematical algorithm that just spews out statistics and that we should not worry about what it is supposed to represent. That's easy: you avoid the discussion.

There's a whole class of different views, but it seems always to implicitly accept that an observer is associated to ONE brain state. Actually the view I have exposed is a bit deviant from the majority of MWI versions: in most MWI versions, all the different terms are "equally valid" and you just "happen to be one of them, at random". The problem most of these approaches have is to derive the correct Born rule for the probabilities, but there are several schemes that, with additional (sometimes not realized) assumptions, one can arrive at "effective Born rules", or because the number of states that count are to be distributed in exactly that way, or because some states of small amplitude are not supposed to count, or because of some game theoretical arguments or whatever.

Is there a problem with energy conservation in a unitary evolution ? Don't forget that what is called "different worlds" are just the different terms in the wavefunction !

I don't think you are having a problem with writing the state of an electron as a superposition of momentum states, and then wonder where all these momenta come from in the different terms. Is there no momentum conservation ? Do we now have many times the original momentum of the electron because it is in a superposition of momentum states ? That's because you don't ADD them.

A less spectacular name for it is "relative state interpretation". If you go on the quant-ph archive and do a search on that, you'll find tons of papers.

EDIT:
As to your "I have had a hard time getting anyone to talk about it.", I think that is because MWI-ers are a bit affraid to be dumped as lunatics or crackpots by the Copenhagen crowd. It doesn't sit well within the macho physicist culture to "talk philosophy" sometimes. You have to be down-to-earth and hard on maths. I will not hide that it DOES sound outlandish at first. But the more you read about it, and the more you think about it, the more natural it seems to become.

Last edited: Jan 20, 2006
17. Jan 20, 2006

### vanesch

Staff Emeritus
I think that we are on-topic, no ? Considering the physicist as part of the quantum system is exactly what MWI is all about, no ?

18. Jan 20, 2006

### Ivan Seeking

Staff Emeritus
No doubt.

As for the energy, could I be thinking of another model that would "create" another universe for each choice in this one?

Anyway, I need to review some of my old stuff and your posts... I wasn't ready for this.

I would love to see and have an in-depth discussion here.

Last edited: Jan 20, 2006
19. Jan 20, 2006

### quantumcarl

I'd say the thread is right on track.

You physicist types are siting studies and theories that explore the idea of how the experimentor could be viewed as one of the instruments in an experiment.

I may have been a bit harshdemanding urine samples, EEG and EKG readings, DNA samples and CAT scans along with eye exams and dream analysis' of practising physicists.

I think in the end I could have simply asked for an explaination about how much a physicist will objectively scrutinize and include their presence and those effects of the condition of their presence on an experimente and its final, observed outcomes. And that question is being explored and answered.

Thank you for the great amount of detail being brought to this thread.

Last edited: Jan 20, 2006